Relationships Between Protein Supplies and B-Vitamin Requirements, in Axenically Cultured Drosophila

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Abstract
The problem of the relationship between dietary protein levels and vitamin requirements has been examined using germfree Drosophila, cultured with defined diets. Four and 7% casein were selected as the two test levels, since growth rate was the same with both. All vitamins, other than that under test, were provided in excess, and the other constituents were the same in both diets. Dose-responses determined simultaneously with the two diets, showed that requirements of thiamine and of riboflavin were not affected by these protein levels. Requirements of pyridoxine were increased fourfold with the 7% casein diet, and in rough proportion to the amount of casein. Nicotinic acid needs increased to about three times that necessary with the 4 % casein diet, but little, if at all, with a 5% casein diet. The increased requirement was apparently involved in the metabolism of the extra tryptophan and glutamic acid provided by the higher protein diet, since supplements of these amino acids each increased the nicotinic acid minimum. Pantothenic acid requirements were almost doubled at the higher protein level, possibly as a consequence of a higher rate of fat synthesis from ketogenic amino acids. Oleic acid spared, and fructose increased, requirements of pantothenate. Biotin requirements were also increased with the protein level, but oleic acid (provided as Tween 80) spared all except a minor, essential fraction of the biotin requirement. Folic acid requirements were increased about 5 times with the higher protein supply, most of which can apparently be accounted for by the conversion of glycine to serine. Dietary serine could substitute for part of the folic acid supply. The results were discussed in the light of previous observations, and the reason adduced for the discordance of earlier observations. The importance of taking account of the total pattern of metablism resulting from dietary changes was stressed, particularly with respect to statements concerning minimal supplies of vitamins and to comparisons of requirements of different organisms.